The present invention relates to wafer etching systems, such as Plasma Assisted Chemical Etching (PACE) systems. More particularly, the present invention relates to a gas discharge apparatus having modified components such that particulate matter and etch by-products generated during the etching process are easily evacuated from the PACE system and substrate surface being etched and resulting substrate contamination is minimized.
Conventional PACE systems are used to etch or figure the surfaces of substrates generally after a rough mechanical grinding and rough polishing step. The PACE process generally uses a gas discharge apparatus having an electrode which is positioned above a substrate to be figured. Radio frequency (RF) power is fed to the electrode and through a positioning table supporting the substrate. A reactive gas flows through the electrode where it is ionized and generates a chemically reactive plasma species which is then discharged onto the surface of the wafer. This plasma discharge chemically reacts with and figures the surface of the wafer to a predetermined shape and/or thickness value.
The shape of the RF generated plasma used to etch the surface is defined by the design of the RF electrode. As the generated plasma moves across the substrate surface and removes material from the surface, particulate matter and etch by-products are generated. Particulate matter, or particulates, can consist of solid matter, gaseous etching by-products, plasma by-products, and ions. The generated matter is evacuated from the plasma combustion chamber of the electrode by means of being entrained in the flow stream from the gas forming the plasma as the excess gas is exhausted via a vacuum pump attached to the PACE reactor chamber away from the substrate surface.
The majority of the plasma generated particulates are removed from the region near the plasma via the flow stream from the gas used to form the plasma. The design of current gas discharge apparatuses, however, limits the ability of the system to effectively remove all particulate matter generated by the figuring of the substrate. Current designs of the annular outer chimney, annular outer chimney clamp, and annular insulator collar portions of the gas discharge apparatus can inhibit the flow of the particulate matter away from the plasma region and substrate surface. These components currently limit the flow of particles in that these particles either contact the annular outer chimney, annular outer chimney clamp or annular insulator collar and, hence, are inhibited from free movement. As the flow of the particulate matter is inhibited, the particulates may contact, and subsequently attach to, the wafer surface. Any particles left on the wafer surface may be subsequently etched away at a different rate than the surrounding silicon. Hence, although the particle is removed, a bump or hill of silicon is left behind on the wafer surface. Such irregularities on the wafer surface can cause numerous problems during the subsequent manufacturing process and device fabrication.
Therefore, a need exists for a design of a gas discharge apparatus for use in a PACE system that can effectively allow generated particulate matter to be removed from the substrate surface and plasma region such that unwanted particulate matter deposited on the wafer is minimized or eliminated.